Slurry polymerization reactor

ABSTRACT

A chemical reactor for slurry polymerization comprising: A. A GENERALLY CYLINDRICAL VESSEL HAVING A CIRCULAR CROSSSECTION; B. A GENERALLY CYLINDRICAL, ROTATABLE, OPEN-CAGE, SPIRALFLIGHTED, RIBBON ELEMENT COAXIALLY MOUNTED INSIDE OF THE VESSEL, HAVING A DIAMETER SLIGHTLY SMALLER THAN THE INSIDE DIAMETER OF THE CORRESPONDING PART OF THE VESSEL WHEREIN IT ROTATES; AND C. A ROD ELEMENT POSITIONED ADJACENT TO THE INSIDE SURFACE OF THE RIBBON AND MOUNTED IN SAID REACTOR VESSEL INDEPENDENTLY OF SAID RIBBON ELEMENT SO THAT, DURING ROTATION OF SAID RIBBON ELEMENT, RELATIVE MOTION OCCURS BETWEEN THE ROD AND RIBBON ELEMENTS, THE ROD AND RIBBON ELEMENTS COOPERATING AND ARRANGED SUCH THAT SAID RELATIVE MOTION PRODUCES A SCRAPING ACTION TO REMOVE AGGLOMERATED MATERIAL ADHERING TO THE INSIDE SURFACE OF THE RIBBON.

United StatesPatent [19 Anolick et a1.

[451 7 Apr. 2, 1974 SLURRY POLYMERIZATION REACTOR [73] Assignee: E. I.du Ponte de Nemours and Company, Wilmington, Del.

[22] Filed: Apr. 5, 1972 [2]] Appl. No.: 241,239

Related U.S. Application Data [63] Continuation-impart of Ser. No.873,353, Nov. 3,

1969, abandoned.

[56] References Cited UNITED STATES PATENTS 3,113,843 12/1963 Li 23/2851,951,996 3/1934 Schaefer 165/92 3,361,537 1/1968 Ferrante 23/2833,549,334 12/1970 Schneider et a1. 23/285 Primary Examiner.lames H.Tayman, Jr.

[57] ABSTRACT A chemical reactor for slurry polymerization comprising:

a. a generally cylindrical vessel having a circular cross-section;

b. a generally cylindrical, rotatable, open-cage, spiral-flighted,ribbon element coaxially mounted inside of the vessel, having a diameterslightly smaller than the inside diameter of the corresponding part ofthe vessel wherein it rotates; and

c. a rod element positioned adjacent to the inside surface of the ribbonand mounted in said reactor vessel independently of said ribbon elementso that, during rotation of said ribbon element, relative motion occursbetween the rod and ribbon elements, the rod and ribbon elementscooperating and arranged such that said relative motion produces ascraping action to remove agglomerated material adhering to the insidesurface of the ribbon.

7 Claims, 1 Drawing Figure SLURRY POLYMERIZATION REACTOR CROSS-REFERENCETO RELATED APPLICATIONS This application is a continuation-in-part ofapplication Ser. No. 873,353, filed Nov. 3, 1969, entitled ChemicalReactor, now abandoned.

BACKGROUND OF THE INVENTION The cost of manufacturing elastomers in asolution polymerization process is greatly influenced by the cost ofisolating the elastomer from the solvent and its recovery and the costof the solvent used. In addition, practical means of handling thepolymer solution dictate that the viscosity of the reaction mass in thereactor be low which in turn limits the polymer concentrationobtainable. Unreacted monomers when separated from the polymer duringrecovery are desirably recycled to the reactor to make the processeconomical.

It is known that polymerization can be performed in a slurry" process bycopolymerizing monomers in a selected non-solvent for the polymer suchas a halogenated hydrocarbon solution as described in US. Pat. No.3,291,780 or by copolymerizing the monomers in the liquid monomersthemselves as disclosed in US. Pat. Nos. 3,370,052 and 3,358,055. Aslurry process, particularly one using a liquid monomer reaction medium,has the advantages of requiring a smaller reactor volume throughput perunit of polymer produced than a solution process and a higher reactionrate per unit amount of catalyst. These advantages translated into acommercial process permit the use of a smaller reactor per unit ofpolymer produced and mass transfer problems and mixing are minimizedbecause of the lower viscosity of the reaction medium compared to thesolution process. In addition, the absence of a solvent eliminates thethe need for solvent isolation and recycle equipment minimizing the costfor equipment needed for polymer isolation and purification. 1

Although slurry polymerization has many advantages, it does have onemajor disadvantage. When the elastomeric copolymer thus prepared sticksto the reactor walls and surfaces in contact with themedium, it foulsthe reactor.

British Pat. No. 1,097,282discloses a polymerization reaction mass intoa vertical extruder. This apparatus is suggested for mixing in themanufacture of polymers such as nylon (polyhexamethylene adiparnide)which is maintained in a molten state in the reactor and leaves thereactor by gravity flow.

This reactor is not useful for preparing elastomeric copolymers by aslurry process because these copolymers are generally sticky materialswhich will not flow out of the reactor readily. The viscoelastic polymeragglomerates in the reactor and sticks to the spiral ribbon and thesides ofthe reactor, eventually fouling it.

There is a need fora chemical reactor for carrying out a slurry"polymerization process whereby the causing reactor fouling.

SUMMARY OF THE INVENTION This invention provides a chemical reactorcomprising: I

a. a generally cylindrical vessel having a circular cross-section;

b. a generally cylindrical, rotatable, open-cage, spiral-flighted,ribbon element which is coaxially mounted inside the vessel, having adiameterslightly smaller than the inside diameter of the correspondingpart of the vessel wherein it rotates; and

c. a rod element positioned adjacent to the inside surface of theribbon'and mounted independently of said ribbon element in said reactorvessel so that, during rotation of said ribbon element, relative motionoccurs between the rod and ribbon elements, the rod and ribbon elementscooperating and arranged such that said relative motion produces ascraping action to remove agglomerated material adhering to the insidesurface 0 the ribbon.

The rod can have a cross-section of any configuration, e.g., elliptical,circular, rectangular, triangular, etc. The rod can be fixed, rotated onits axis counter to the direction of ribbon rotation, or rotated on itsaxis in the same direction of ribbon rotation provided that relativemotion occurs between the rod and the-inside surface of the ribbon. In apreferred embodiment the rod 'rotates counter to the direction of and attwice the speed of ribbon rotation.

DESCRIPTION OFTHE DRAWINGS with an extruder. The apparatus is showntogether with a flow pattern of a polymerization process;

DETAILS OF THE INVENTION Referring to the FIGURE of the drawing, theapparatus of this invention consists'essentially of a generallycylindrical, vertically aligned vessel 1, with a circular cross-sectionhaving a polymerization section 2 and a polymer qcollecting section- 3-incommunication with each other. Polymerization section '2 i's made of acylindrical section 4 and a truncated cone section 5 and houses anopen-cage, double-flighted spiral ribbon 6. The polymer collectingsection houses an extruder 7. Alternatively, reactor 1 can behorizontally aligned or canted and the spiral ribbon can be single ormultiple flighted. Y

The spiral ribbon is rotatably mounted and has an outside diameterslightly smaller than the inside diameter of vessel 1 so that it almostscrapes the walls of the polymerization, region 2 as it rotates. Theribbon is rotated by conventional driving means (not shown) connected tothe central shaft portion of extruder 7, to which the ribbon is rigidlysecured. It is desirable to maintain sufficient clearance between thespiral ribbon 6 and vessel 1 to avoid mechanically binding the spiralribbon. The amount of clearance A can vary according tothe type polymerbeing prepared and the amount of polymer build-up permissible forcontinuous operation. In preparing an ethylene/propylene/l,4-hexadienepolymer (58/36/6) in a reactor having an inside diameter of 8.9 cm. thespiral ribbon desirably has a clearance of about'0.32 cm. from theinside wall of vessel. 1. The pitch of the spiral ribbon can be from-V2to 3 ribbon diameters and preferably is %to 1 /2 diameters for optimumeffectiveness. The pitch B is the longitudinal spacing of correspondingpoints on adjacent flights and in the case of multiple flights, thepitch is equal to the longitudinal spacing multiplied by the number offlights. The dimension of the spiral ribbon in the radial direction Cshould be no greater than one-fourth of the largest inside diameter ofvessel 1. The lower end of the spiral ribbon conforms to the conicalsection of the polymerization chamber.

In operation, spiral ribbon 6 simultaneously removes material (e.g.,polymer) adhering to the walls of vessel 1 and moves it to extruder 7which, for practical reasons, usually has a diameter of less thanone-half that of vessel 1, and a flight pitch of about /2 to 2 extruderdiameters. The spiral ribbon and extruder can be joined to rotate at thesame speeds. Also they can be arranged so-that they rotate at differentspeeds.

A stationary rod 9 is placed inside the cage of the spiral ribbon and ispositioned to remove polymer from the inside periphery of the spiralribbon. lt isdesirable to maintain a clearance between rod 9 and thespiral ribbon 6 to avoid mechanically binding the moving parts. Aclearance of up to about 4 percent of the diameter of vessel 1 has beenfound useful.

Rod 9 can be attached at one end to the inside wall of vessel 1 at point10 and at the other end can be free or, if desired, attached to theextruder at point 11 by atbearing (not shown) which permits theextruderto rotate but holds the rod stationary.

Rod 9 can have a cross-section of any one of a num ber of differenttypeconfigurations, e.g., rectangular, square, elliptical, triangular, orcircular; and any one particular cross-section'can be used with varyingthicknesses along the length of the rod for added strength. If duringuse polymer build-up on'the rod becomes excessive, the portion of therod in the conical section can be eliminated or the monomer mixingregion and the polymer collecting region can be made having the samesize cross-section, thereby eliminating the truncated conical sectionand the rod can be rotated on its axis. in such a case, rod 9 isextended beyond the reactor and conventional driving means (not shown)are used to rotate rod 9 on its axis, Particularly desirable results areobtained by rotating rod 9 counter to and at approximately twice thespeed of spiral ribbon 6 rotation.

' The apparatus of this invention is useful in preparing polymerswherein the polymer is a separate phase insolwhere R is hydrogen or C,C,alkyl, preferably straightchained. Representative a-monoolefins arepropylene, i-butene, l-pentene, l-hexene, l-heptene, l-octene,l-octadecene, 6ethyll-dece ne, and S-methyll-hexene.

Other polymers include sulfur curable a-olefin elastomeric copolymers.By sulfur curable it is meant that the copolymer will contain at least0.1 gram moles of ethyle'nic carbon-to-carbon double bonds per kilogram.-ln order to obtain a copolymer with desirable elastomeric properties,it should contain between about 20 to weight percent ethylene units and80-20 weight percent of another a-olefin hydrocarbon.

v Z2 Z3 jizfljziif i i wherein Z is C -C alkylene and Z Z and 2 areindependently hydrogen or alkyl radicals and the Z groups are selectedsuch that the diene has from about 6-22 carbon atoms.

Useful open-chain dienes include l,4-hexadiene, 1,9-

octadecadiene, 6-methyl-1 ,S-heptadiene, and15-ethyll,l5-heptadecadiene. 7

Useful cyclic non-conjugated dienes include dicyclopentadiene 5-alkylidene-2-norbornene e. g. 5-ethylidene-2-norbornene,'5-alkenylsubstituted 2- norbornenes, e.g., 5-(2-butenyll-2-norbomene,2-alkyl-2,5-norbornadienes, e.g. 2-ethyi-2,5- norbornadiene and1,5-cyclooctadiene.

A preferred EPDM copolymer is ethylene/- propylene/ l ,4-hexadiene.

Representative copolymers made from the abovedescribed a-monoolefinsthat can be made using the apparatus of this invention are given in U.S.Pat. Nos. 2,933,480; 3,000,866; 3,063,973; 3,093,620; 3,093,621;3,151,173; and 3,260,708.

The polymer'can be prepared by conventional polymerization techniquesand is conveniently formed by carrying out the polymerization in theliquid monomers to be polymerized. Since the liquid part of the medium.

can contain liquids other than the liquid monomers, it will be referredto, for convenience, asthe liquid organic polymerization medium. Thecatalyst used can be any conventionally known catalystv The polymerforms as a separate phase and contains dissolved and occludedliquidorganic polymerization media. When the polymer phase is formed, itgenerally tends to adhere to the equipment surfaces exposed to thepolymer particles, coalesces, and forms an agglomerated mass. Theagglomerated polymer is removed from the equipment surfaces by therevolving spiralflighted ribbon, collected, and extruded from thereactor.

The occluded portion is removed or expressed by the mechanical action ofkneading or shearing the polymer while still in the reactor andextruder. Pressure increases as the polymer is conveyed through theextruder from reactor pressure to a discharge gauge pressure which isgenerally above 50 kg/cm and preferably between 50 and 150 kg/cmPressure differentials so formed cause occluded liquids, as they arefreed, to move opposite to the direction of extrusion and return to thereactor. Any dissolved portions can be vaporized from the polymer as thepolymer leaves the reactor or can be removed by other conventional meansat a later time.

The operation of this reactor will be described as it is used to preparean elastomeric copolymer of ethylene/propylene/l ,4-hexadiene. Allparts, percentages, and proportions are by weight unless otherwiseindicated.

EXAMPLE 1 The apparatus used to carry out this example is shown in theFIGURE of the drawing. Cylindrical portion 4 of reactor 1 has an insidediameter of 8.89 cm. and a length of 27.9 cm. Truncated conical section5 which serves as a transition between the cylindrical portion 4 and thepolymer collecting region 3 is 3.81 cm. in height with an outsidediameter of 8.81 cm. at one end to match the connecting portion of thepolymer collecting region 3.

The spiral ribbon contained within the polymerization region 2 has anoutside diameter of 8.25 cm. in the cylindrical section of thepolymerization region and spirals in the conical section maintaining aclearance of 0.32 cm. It is double-flighted having a pitch of 17.8 cm.Within the spiral ribbon is stationary rod 9 made of steeland positionedto scrape the inside portion of the spiral ribbon as the ribbon rotates.The polymer collecting region is 41.61 cm. long housing an extruder witha varying diameter, pitch, and flight depth.

The extruder is made up of four sections. Details of the sections arenow shown. The first section is cylindrical having an outsid e diameterof 3.81 cm. to match the small diameter of the truncated conical sectionand a length of 12.4 cm. with flights of 1.11 cm. deep pitched at 3.2cm. The second section is a transitional section having an outsidediameter of 3.81 cm. to match the first section then tapering to adiameter of 2.54 cmpThis transitional section has a length of 6.35 cm.with a flight depth ranging from 1.11 cm. to 0.95 cm. and a pitchvarying from 3.2 cm. to 2.54 cm. respectively. The third section iscylindrical having an outside diameter of 2.54 cm. and a length of 10.98cm. The flight depth is 0.95 cm. with a pitch of 2.54 cm. The fourthsection is 11.88 cm. long having an outside diameter of 2.54 cm. and aflight depth of 0.38 cm. pitched at 2.54 cm. The transition in flightdepth between the third and fourth sections is gradual.

The ingredients are fed to reactor 1 in the following manner: ethylene,propylene, and hydrogen gases are fed to conduit 12 through rotometers(not shown) and directed to the inlet of compressor 16. The average flowrates are as follows: through port 13 passes ethylene at 88.5 grams perhour; through port 14 passes propylene at 437 grams per hour; andthrough port 15 passes ethylene plus 1.73 volume percent hydrogen at 68grams per hour. These gases are then compressed in compressor 16 to apressure of 35.1 kg/cm and then condensed in water-cooled condenser 17at a temperature of 25C. and fed to the conical section of the reactorat 19 through pressure regulating valve 18. A third monomer and thecatalysts are added to the reactor as a liquid. One stream is fed to thereactor through port 20 as a 0.0171 mole per liter solution of vanadiumt'ris(acetylacetonate) in 1,4-hexadiene and another stream is fedthrough port 21 as a 0.639 mole per liter solution of diisobutylaluminumchloride in 1,4- hexadiene. These solutions are fed at a rate of 50'milliliters per hour and 23.5 milliliters per hour, respectively.

The amount of liquid in reactor 1 is maintained at about 1.0 liter. Theliquid level is measured with a gamma radiation source and detector (notshown) and manually controlled to maintain proper volume in the reactor.The liquid monomer temperature in reactor 1 is maintained at C.

Reactor 1 is surrounded by a water jacket 25 having inlet port 26 andexit port 27. The water in the jacket is maintained at approximately C.The water jacket serves to prevent heat loss from the reactor byconduction through the reactor wall due to the large surface to volumeratio of this small scale reactor. The polymerization process isexothermal and the liquid monomer temperature in the reactor ismaintained at 45C. by evaporative cooling. The heat of reaction isremoved by allowing the reaction. liquid to boil. The vapor producedpasses through temperature control valve 24 and into conduit 12 to berecycled with fresh monomers.

The polymer forms as a separate phase which adheres to the reactor andprocessing equipment and agglomerates into a mass. As the spiral ribbonturns, it scrapes the polymer from the sides of the reactor, and thestationary bar 9 scrapes the polymer fromthe inside surface of thespiral ribbon permittingthe helix to pump the polymer to the polymercollecting region 3. Extruder 7 in the polymer collecting chamber pumpsthe polymer to gauge pressures in excess of 50 kg/cm Extruder 7 shearsthe polymer as it'pumps the polymer from the reactor. Occluded monomersare freed from the polymer during shearing of the polymer by spiralribbon 6 and the extruder. The freed monomers migrate upwards, againstthe" direction of .polymer travel, returning to polymerization region2.'Dissolved monomers in the polymer are vaporized as the polymer movesfrom the high pressure area in the extruder output through pressurecontrol valve 22.

' The copolymerization process is continuous for a period of 29 hourswith the production rate of copolymer of about 56 grams per hour. Thereaction is maintained at a temperature of 45C. with a pressure of about21.1

' kg/cm in the vapor space of reactor 1. A typical analysis of the vaporin the reactor is 0.8 percent nitrogen, 0.2 percent hydrogen, 31 percentethylene, and 68 percent propylene. Excess monomers are removed from thereactor through a port (not shown) on the side of the reactor vessel tocontrol the liquid level of the reactor so that the level of the liquidnever exceeds the height of the spiral ribbon.

Analysis of the copolymer discharged from the extruder, but prior toflashing shows that it contains approximately 0.40 gram of dissolvedresidual liquid monomers per gram of dry polymer produced. Anindependent test run under the reaction conditions of this example showsthat the solubility of the liquid monomers in the polymer is 0.40 gramof monomers per gram of dry polymer. Therefore, the presence of 0.40gram of residual liquid monomers show that the entrained or occludedmonomers are expressed or removed from the polymer, in the reactor,before it is discharged from the extruder. The monomers are flashed offand analysis shows that the copolymer average composition is 58.3 weightpercent ethylene, 36.2 weight percent propylene, and 5.41 weight percent1,4- hexadiene and has a Wallace Plasticity of 45.

We claim:

1. A chemical reactor for slurry polymerization comprising:

a. a generally cylindrical vessel having a circular cross-section;

b. a generally cylindrical, rotatable, open-cage, spiral-flighted ribbonelement coaxially mounted inside of the vessel, said ribbon elementhaving a diameter slightly smaller than the inside diameter of thecorresponding part of the vessel wherein it rotates; and a rod elementpositioned adjacent to the inside surface of the ribbon and mounted insaid reaction vessel independently of said ribbon element so that,during rotation of said ribbon element, relative motion occurs betweensaidrod and ribbon elements, the rod and ribbon elements cooperating andarranged such that said relative motion produces a scraping action toremove agglomerated material adhering to the inside surface of saidribbon.

2. The reactor of claim 1 wherein said spiral-flighted ribbon elementhas a flight pitch of about it to 3 ribbon diameters.

3. The reactor of claim 1 wherein the dimension of said spiral-flightedribbon element in the radial direction is no greater than one-fourth ofthe largest diame ter of said vessel.

4. The reactor of claim 1 wherein said rod element is rigidly secured tosaid vessel, and the clearance between said rod and said ribbon elementsis up to 4 percent of the inside diameter of said vessel.

5. The reactor of claim 1 wherein said rod element I is rotated on itsaxis counter to and at approximately twice the speed of the rotation ofsaid ribbon element.

6. The reactor of claim 5 wherein said rod element has a cross-sectionvarying in thickness along the length of the rod.

7. The reactor of claim 1 wherein extruder means cooperate with saidribbon element such that said ribbon element directly feeds the extrudermeans.

2. The reactor of claim 1 wherein said spiral-flighted ribbon elementhas a flight pitch of about 1/2 to 3 ribbon diameters.
 3. The reactor ofclaim 1 wherein the dimension of said spiral-flighted ribbon element inthe radial direction is no greater than one-fourth of the largestdiameter of said vessel.
 4. The reactor of claim 1 wherein said rodelement is rigidly secured to said vessel, and the clearance betweensaid rod and said ribbon elements is up to 4 percent of the insidediameter of said vessel.
 5. The reactor of claim 1 wherein said rodelement is rotated on its axis counter to and at approximately twice thespeed of the rotation of said ribbon element.
 6. The reactor of claim 5wherein said rod element has a cross-section varying in thickness alongthe length of the rod.
 7. The reactor of claim 1 wherein extruder meanscooperate with said ribbon element such that said ribbon elementdirectly feeds the extruder means.